Add composable / filtered candidate locators (chained locator)

[JE-Chen]

anchor_locator is a single anchor→target relation and grid_locator addresses cells — neither supports composable refinement of a candidate set (.within(panel).filter(has_text='Delete').nth(2)), the Selenium-4 / Playwright chained-and-filtered locator idiom.

• from_boxes(boxes) → Candidates: a pure post-filter over boxes from any source (template / OCR / a11y / fuse_elements). Methods within (region clip), filter (has_text / near / min_area / max_area / predicate), sort_reading, nth / first / last, resolve(), center(). Every method returns a NEW Candidates (no mutation).
• AC_locate_chain applies a JSON ops list to a boxes array → {count, boxes, center}.
• Pure-stdlib; reuses element_parse.reading_order for sort_reading (no dup). Fully headless-testable. Wired through all 5 layers + headless test + EN/Zh docs + WHATS_NEW. Qt-free.

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[codacy-production]

Not up to standards ⛔

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